ISPN-3318 Add embedded rolling upgrade documentation

* Command-Line Interface cache loader will be documented in a
separate commit.
ISPN-3400 Update JCache documentation
ISPN-3534 Investigate performance regressions in Infinispan 6.0.0

Set the default UFC.max_credits and MFC.max_credits to 2M, which is also
the JGroups default.
ISPN-3708 Allow setting a default cache for the Protocol servers
Minor documentation corrections
ISPN-3615 Add user documentation for Infinispan's new query DSL